ENTOMOLOGISK TIDSKRIFT I913. 



Summary. 



It has been a great puzzle to many entomologists who 

 have studied the lite-history of the leaf-miners that in the 

 autumn the parts of the leaf occupied by the mines retain 

 their green colour for a long time after the rest of the leaf 

 has turned yellow and died. 



Wood (1894, p. 153) attempted to show that the phe- 

 nomenon was caused by some preservative substance pro- 

 duced by the larva and his theory has subsequently become 

 generally accepted and even considered a proven fact. 



This theory does not, however, pay the slightest atten- 

 tion to the physiological processes which take place in the 

 leaves when in the autumn they turn yellow and finally drop 

 off to the ground. During this time a part of the sap, con- 

 taining iron, magnesium and phosphoric acid flovv's back to 

 the trunk. If, however, by cutting the nervule of the leaf 

 this process is prevented in the part of the leaf situated 

 beyond the cut, this part of the leaf remains green because 

 it cannot get rid of the substances above mentioned. 



In the light of these facts it seemed highly probable 

 that in the same way the mines where caused to remain 

 green simply because they interfered with the flowing back 

 of the sap of the leaves, having injured or annihilated the 

 vascular bundles in certain parts of the leaves. 



In order to put this hypothesis to a test two mines of 

 a different type, both very conimon on oak-leaves in the 

 autumn in the neighbourhood of Stockholm, were examined 

 and sectioned. The result of this investigation was that the 

 features displayed by the leaves as regards the position and 

 size of the green patches were exactly those which, to judge 

 from the anatomy of the mines, it was possible to calcu- 

 late, based on the assumption that their action was simply 

 to interfere to a smaller or greater extent with the passage 

 of the sap in the leaves. 



The mine of Lithocollctis (fig. i) is a blotch-mine of a 

 regular oval shape; it is already from the beginning exca- 

 vated as a blotch which becomes gradually wider until it 



